Deuteronomy 4:10-12

10Remember the day you stood before the Lord your God at Horeb, when the Lord said to me, ‘Assemble the people to Me, that I may have them hear My words 1so that they may learn to 2fear Me all the days that they live on the earth, and that they may 3teach their children.’

11You came forward and stood at the foot of the mountain, 4and the mountain was burning with fire to the heart of the heavens: darkness, cloud, and thick gloom.

12Then the Lord spoke to you from the midst of the fire; you heard the sound of words, but you saw no form--there was only a voice.